Viability of the endothelium of donor corneal tissue used for penetrating keratoplasty is essential if the grafted tissue is to maintain transparency. Many questions regarding the suitability of fresh or cryopreserved donor tissue for full thickness grafting remain unanswered because no simple technique is yet available for accurately assessing endothelial viability. The objectives of the proposed research are: (1) to evaluate changes in corneal endothelial ultrastructure due to the various factors involved in the selection, storage and preservation of donor corneal tissue; (2) to relate these changes to other assessments of endothelial viability; and (3) to apply the results of these studies to the development of a more rational approach to the selection, storage and preservation of donor corneal tissue. The methods that will be used for functional studies include radioautography, histochemical enzyme and vital staining, measurements of oxygen consumption, and specular microscopy. Short and medium-term methods of corneal preservation, such as in physiological solutions of varying compositions and organ culture, will be evaluated and compared.